RAT LUNG ALVEOLAR TYPE-II CELL-LINE MAINTAINS SODIUM-TRANSPORT CHARACTERISTICS OF PRIMARY CULTURE

Culture of primary alveolar type II cells has been widely used to inve stigate the Na+ transport characteristics of alveolar epithelium. Howe ver, this model was restricted by early morphological and physiologica l dedifferentiation in culture. Recently, a cell line has been obtaine d by transfection of neonatal type II cells with the simian virus SV40 large T antigen gene (SV40-T2). SV40-T2 cells have retained prolifera tive characteristics of the primary type II cells (Clement et al., 199 1, Exp. Cell Res., 196:198-205.) In the present study, we have charact erized Na+ transport pathways in SV40-T2 cells. SV40-T2 cells retained most cardinal properties of the original alveolar epithelial cells. N a+ entry occurred, as in primary cultures, through both Na+-cotranspor ters and amiloride-sensitive Na+ channels. SV40-T2 cells expressed Na-phosphate, Na+-amino acid and Na+-K+-Cl- cotransports which are quant itatively similar to that of primary cultures. The existence of amilor ide-sensitive Na+ channels was supported by molecular and functional d ata. SV40-T2 expressed the cloned alpha- and gamma-mRNAs for the rat e pithelial Na+ channel (rENaC), whereas beta subunit was not detected, and Na-22(+) influx was significantly inhibited by 10 mu M amiloride. Na+, which enters SV40-T2 cells, is extruded through a Na+, K+-ATPase- mRNA for alpha, and beta(1) isoforms of Na+, K+-ATPase were present an d Na+, K+-ATPase activity was evidenced either on intact cells by the presence of a ouabain-sensitive component of Rb-86(+) influx ol on cel l homogenates by the measurement of ouabain-inhibitable ATP hydrolysis . These results indicate that SV40-T2 cell line displays most of the N a+ transport characteristics of well-differentiated primary cells in t he first days of culture. We conclude that the SV40-T2 cell line provi des a model of differentiated alveolar type II cells and may be a powe rful tool to study, in vitro, the modulation of Na+ transport in patho physiological conditions. (C) 1996 Wiley-Liss, Inc.